Silver Lake WTP Clearwell Part 2 The Tracer Study PHOTO OPTIONAL. NEWWA 2009 Spring Joint Regional Conference and Exhibition The Value of Water

Transcription

1 Silver Lake WTP Clearwell Part 2 The Tracer Study NEWWA 2009 Spring Joint Regional Conference and Exhibition The Value of Water PHOTO OPTIONAL Louis Soracco, P.E. April, 2009

2 Discussion Format Background Computational Fluid Dynamic (CFD) Model Tracer Study Equipment Setup and Procedures Sampling Locations and Frequency Accuracy Verification Tracer Study Results Comparison to the CFD Model Conclusions Questions and Answers

3 Background Originally constructed in 1966 Surface water treatment source for City of Brockton 10.7 MGD treatment capacity (typical high flow) Utilizes ~1.1 MG finished water clearwell for chlorine contact time Veolia Water is the current WTP Operator Clearwell was previously un-baffled with a baffle factor of 0.4 Baffle curtains were designed and installed Final condition of DEP approval was to conduct a tracer study to confirm C t and baffle factor

4 Computational Fluid Dynamics (CFD) One of the branches of fluid mechanics that uses numerical methods and algorithms to solve and analyze problems that involve fluid flows. Computers are used to perform the millions of calculations required to simulate the interaction of fluids and gases with the complex surfaces used in engineering. Source: wikipedia.org

5 CFD Model Used to simulate flow through clearwell to determine hydraulic efficiencies of a given arrangement Factors used to measure hydraulic efficiency T 10 = Time for 10% of reservoir volume to pass the specified location T t = Theoretical residence time (Reservoir volume/discharge rate) Contact Time (Chlorine dosages) T 10 /T t = Hydraulic Efficiency

6 Examples of Hydraulic Efficiency Baffling Condition T 10 /T t Value Un-baffled, mixed flow: very low length-to-width ratio: high inlet and 0.1 outlet flow velocities Poor baffling: single or multiple un-baffled inlets and outlets; no interiorbasin baffles. 0.3 Average baffling; baffled inlet or outlet with some interior-basin baffles. 0.5 Superior baffling; perforated inlet baffle serpentine or perforated interiorbasin baffles, outlet weir, or perforated launders. 0.7 Perfect (plug flow); very high length-to-width ratio (pipeline flow), 1 perforated inlet, outlet, and interior-basin baffles. Source: The Standards and Guidelines for Municipal Water, Wastewater, and Storm Drainage Systems, AENV 1997

7 Existing Conditions CFD Model Plan View

8 Existing Conditions - Simulation

9 Final Configuration

10 Final Configuration 200 L.F. - Simulation

11 Existing Conditions vs. New Baffle System Existing Conditions T 10 /T t = 0.42 Contact Time = 64.6 minutes (10.25 MGD) Clearwell with Baffle Curtains Installed T 10 /T t = 0.66 Contact Time = minutes (10.25 MGD) 57% increase from existing conditions

12 Tracer Study Equipment Injection Location Equipment Sodium Fluoride (NaF) 55 gallon batch drum Scale and data logger Peristaltic chemical feed pump Sampling Location 1 Equipment Discharge of high head pump Probe calibrated to measure conductance of water in millivolts (change in mv = surrogate to change in Fluoride concentration) Data logger Sampling Location 2 Equipment WTP Laboratory Probe calibrated to measure millivolts

13 Tracer Study Setup Tracer Chemical Used Sodium Fluoride (NaF) Injection Location Equipment Backwash pump chamber Sampling location 1 Sample port at discharge of high head pump Sampling Location 2 WTP Laboratory

14 Tracer Equipment and Setup Photos Backwash Pump Chamber Access Hatch Finish Water High Head Pumps

15 Tracer Equipment and Setup Photos NaF Feed System NaF Feed Pump and Data Logger

16 Tracer Equipment and Setup Photos High Head Pump Discharge Sample Location 1 Data Logger

17 Tracer Equipment and Setup Photos Sampling Probe Readout Sampling Probe

18 Tracer Study Overview The WTP routinely operates at two flow rates Low Flow: 7.3 MGD High Flow: 10.7 MGD During emergencies the WTP will pump more Stresses distribution system Two separate tracer tests were conducted August 20, :15pm 12am (Low Flow) August 21, :30am 12:15pm (High Flow)

19 Tracer Study General Procedure Batch Solution Chemical dosed for a concentration of 1 mg/l Begin Data Loggers Record Residual/Background Fluoride Levels Commence Chemical Injection Monitor Probes Anticipated appearance of Fluoride Re-Batch Solutions if necessary Discontinue chemical injection Continue to monitor levels Allow clearwell to flush clean overnight for next test

20 Tracer Study Flow Diagram

21 Tracer Study Sampling and Verification Sampling Location 1 at discharge to high head pump Periodic samples were taken through each test Sample taken to certified laboratory Samples taken to verify accuracy of probe Sampling Location 2 at WTP Laboratory Served as a backup to main sampling probe Readings lagged due to longer distance

22 7.3 MGD Tracer Sampling Results Charts provided by: Aquaterra (South Burlington, VT)

23 10.7 MGD Tracer Sampling Results Charts provided by: Aquaterra (South Burlington, VT)

24 Tracer Study Results Low Flow (7.3 MGD) Test C t = 183 minutes Baffle Factor = 0.64 High Flow (10.7 MGD) Test C t = 113 minutes Baffle Factor = 0.58 Average Baffle Factor 0.61

25 Revised Contact Time 200 Clearwell Contact Time for a 0.61 Baffle Factor Silver Lake Water Treatment Plant City of Brockton, MA MGD, 173 min. 160 Time (Minutes) MGD, 118 min Flow (MGD)

26 Chlorine Residual Example Table

27 CFD Model vs. Tracer Study CFD Model Baffle Factor = 0.66 Contact Time = 143 Minutes (7.3 MGD) Contact Time = 97.7 minutes (10.7 MGD) Tracer Study Baffle Factor = 0.61 Contact Time = 173 minutes (7.3 MGD) Contact Time = 118 minutes (10.7 MGD)

28 Difference Between Tracer Study and CFD Model CFD Model Intended to improve baffling factor within clearwell only Backwash pump chamber and finished water pump chambers excluded from Model No modifications were proposed Not necessary to determine relative efficiency between potential installation configurations Tracer Study Needed an injection point Backwash pump chamber first practical Needed a sampling point Sampling tap on high head pump discharge was closest practical

29 Tracer Study Additional Volumes

30 Conclusions CDF modeling is a cost efficient and effective tool for designing baffling systems Small variation between model and actual installation Variation caused by additional volumes used in tracer study Limited access prevents exact comparison The type of baffle curtain installed is cost efficient Allowed for installation without taking plant off-line Less than two week installation time Material effectively simulates a wall based on tracer test results Approximately doubled the contact time using existing clearwell Improved water quality by minimizing pockets of old water Project brought both Economic Strength to the Community and improved the overall quality of life through improved treatment

31 Current Status Tracer Report currently under review at the DEP After acceptance of report: WTP operation can take advantage of new contact times Reduction in chlorine usage Should decrease THM and HAA5 formation potential

32 Special Thanks City of Brockton For their cooperation during the study Veolia Water For the opportunity to be involved in this project Michael Sessine (Project Manager) and the rest of the staff for their cooperation during the study Aquaterra Roland Luxenberg for providing all of the equipment, chemicals, sampling results and tracer study experience necessary for the successful execution of the study

33 Questions?